Modal analysis and testing

Photo: Measuring the transfer function between an instrumented hammer

Measuring the transfer function between an instrumented hammer and an accelerometer

Modal Analysis is the study the dynamic response of machines or structures, i.e. the way they vibrate and their frequencies, when excited by a vibrating force or impact.

ISVR Consulting has all the tools necessary for detailed modal analysis of most structures.  In recent times a wide variety of structures has been successfully tested, ranging from a 6 metre steel beam with additions weighing 13 tons, to a small plastic disk of a few millimetres diameter, which is part of a Bluetooth headset.  Modal analysis of existing structural components and prototypes allows potential problems to be seen, with slow-motion video animation of selected modes.

A complete set of transfer functions between the force and response of the structure is taken on a grid sufficient to give a realistic visual interpretation of the potential motion of a test piece.  Either an appropriate vibration exciter or the impact from an instrumented hammer may be used to excite the structure.

Measurements are made using a Brüel & Kjær “PULSE” system, with associated instrumentation according to the size and complexity of the test object.  Results of the measurements are analysed using the Modal Analysis software – ISVR Consulting currently use “ME'scope” from Vibrant Technology.

Operational deflection shapes

ISVR Consulting is also able to measure operational deflection modes on a structure which is subject to external forces which cannot be measured. Frequency response functions between a fixed accelerometer and other fixed or roving accelerometers can be animated in the frequency or time domain, thus illustrating, for example, the response of a vehicle driving over a rough surface, or bumps. This would enable visualisation of the suspension behaviour above and below the natural frequency of the suspension, for instance.